A mechanical seal is a device which is used to prevent fluid leakage from equipment which has a fixed cavity, containing the fluid, and a rotatable shaft. In practice, such a seal is usually situated at a point where the rotatable shaft enters (or leaves) the stationary part of the equipment. Rotary mixers, agitators and pumping devices are typical examples of the type of equipment in which a mechanical seal might be used.
Mechanical seals comprise two distinctly separate sets of components, those which rotate with the shaft of the equipment on which the seal is mounted (the rotary parts) and those which are fixed relative to the stationary equipment body (the stationary parts). The interface between these two sets of components comprises two contacting seal faces, a rotary and a stationary face. These faces are normally manufactured to precise, very accurate standards.
In order for a mechanical seal to function correctly, the two seal faces must be kept in constant contact with one another. To achieve this, it is usual for a seal to include one or more springs, which act as biasing means to urge the seal faces together. In a "stationary type" seal, the spring or springs act against the stationary seal face to urge it towards the rotary face. In a "rotary type" seal, the spring or springs act against the rotary face, to urge it towards the stationary face.
When a spring is compressed, it is able to exert a force which can then act to urge one seal face against another. A spring is thus installed in a mechanical seal in a compressed state. However, it is a consequence of spring design that as its degree of compression increases, so too, proportionately, does the force which it is able to exert (the so-called "spring rate" phenomenon). This, together with the tendency of a spring always to return to its original (i.e. unloaded or de-compressed) shape, can make a mechanical seal rather difficult to assemble. The spring or springs which need to be loaded into the seal can often fall out of their housings during assembly.
The difficulty of assembling a mechanical seal is, to a certain extent, dependent upon the seal design. For example, the problem is eliminated for pre-assembled cartridge seals, which are assembled in the factory prior to use. However, multi-component seals must be assembled in situ on the equipment to be sealed, and problems of spring retention are then exacerbated. Probably the most problematic seal to assemble on an item of equipment is the split seal.
For most split seals, in addition to the spring-related assembly problems, there are additional fitting complications due to all of the seal components being split into two halves. A typical split seal has twice the number of major seal components than its more conventional un-split counterpart. Clearly for a split seal, a spring retaining device would assist in simplifying the complicated assembly process.
It would therefore be useful to provide a spring retaining device, of use in securing a spring or springs in position inside a mechanical seal during its assembly.